A cellular network may comprise multiple access nodes each of which serving one or more terminals. For example, a heterogenous Long Term Evolution (LTE) radio access network comprises access nodes embodied as macro eNodeBs serving a larger serving area compared to access nodes embodied as pico eNodeBs serving a small serving area typically located within the serving area of one macro eNodeB. An association between a terminal and its serving access node may be based on a signal strength of a downlink signal, for example a Reference Signal Received Power (RSRP) in LTE.
Interference effects may arise for a terminal located in a serving area of an access node, since on the one hand a measured signal strength of a signal from the serving access node and therefore a signal quality of the signal decreases with an increasing distance from the serving access node and on the other hand a signal strength of another signal causing interference from another non serving access node increases with the distance from the serving access node. In the above example of LTE, a terminal farer away from its serving pico eNodeB may experience a negative signal quality in terms of a Signal to Interference and Noise Ratio (SINR) determined in a logarithmic domain, since an interference from a macro eNodeB may be stronger than a useful signal from the pico eNodeB. Accordingly, an achievable transmission rate and throughput of such a terminal may be reduced. A failure of a radio link between the terminal and the serving access node may even occur, if the terminal might not be longer able to properly receive control information from the serving access node, for example on the control channel defined in LTE. The aforementioned interference effects may even be worse in a case in which a serving area extension mechanism can be applied for the access node. For example, in a Cell Range Extension (CRE) approach known in LTE, a bias is added to the signal strength of a signal from a pico eNodeB such that a terminal measuring the signal strength may experience the pico eNodeB as best serving access node even at locations outside of the usual serving area of the pico eNodeB. Terminals in the extended serving area range may be particularly subject to interference caused by non-serving access nodes.
In order to address the above interference problems, techniques for interference protection may be used in the cellular network. One technique employs a resource pattern to be applied by an access node which may comprise first resource units reserved for terminals servable by the access node and second resource units reserved for other terminals servable by another access node. For example, in Third Generation Partnership Project (3GPP) for example TS36.423 V11.5.0 (2013-06), a time-frequency resource pattern with Protected Sub-Frames (PSF) is defined for LTE. Such a PSF resource pattern comprises first resource units usable by terminals servable by a macro eNodeB, and second resource units usable by terminals servable by one or more pico eNodeBs. The macro eNodeB may semi-statically not perform Physical Downlink Shared Channel (PDSCH) and Physical Downlink Control Channel (PDCCH) transmission in the second resource units reserved for the terminals servable by the one or more pico eNodeBs such that the pico eNodeBs may use these resources to perform a correct interference measurement and schedule those terminals which would otherwise be strongly affected by interference from the macro eNodeB when not using the described resource pattern.
However, applying an interference protection mechanism such as the above described resource pattern may reduce a throughput of terminals served by the serving access node, since an amount of resources in the resource pattern usable by terminals served by the serving access node may be limited owing to a definition of the second resource units in the resource pattern.
The above situation may even be worse in a cellular network scenario comprising multiple adjacent access node each of which applying its own resource pattern, since a terminal served by an access node and using the second resource units of the resource pattern defined by another access node may experience interference from a further adjacent access node applying a different resource pattern compared to the resource pattern of the another access node. Having defined an identical resource pattern by each adjacent access node may also induce unnecessary resource restrictions for terminals served by one specific access node for a specific traffic situation in that the amount of resources usable by terminals of a particular access node would be even more reduced.